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springboot2.x防XSS攻击 springboot2.x使用Jsoup防XSS攻击的实现

撸小鱼   2021-04-21 我要评论

后端应用经常接收各种信息参数,例如评论,回复等文本内容。除了一些场景下面,可以特定接受的富文本标签和属性之外(如:b,ul,li,h1, h2, h3...),需要过滤掉危险的字符和标签,防止xss攻击。

一、什么是XSS?

看完这个,应该有一个大致的概念。

XSS攻击常识及常见的XSS攻击脚本汇总
XSS过滤速查表

二、准则

  • 永远不要相信用户的输入和请求的参数(包括文字、上传等一切内容)
  • 参考第1条

三、实现做法

结合具体业务场景,对相应内容进行过滤,这里使用Jsoup。

jsoup是一款Java的HTML解析器。Jsoup提供的Whitelist(白名单)对文本内容进行过滤,过滤掉字符、属性,但是又保留必要的富文本格式。
如,白名单中允许b标签存在(并且不允许b标签带有其他属性)那么在一段Html内容,在过滤之后,会变成:

过滤前:

<b style="xxx" onclick="<script>alert(0);</script>">abc</>

过滤后: 

<b>abc</b>

Whitelist主要方法说明

方法 说明
addAttributes(String tag, String... attributes) 给标签添加属性。Tag是属性名,keys对应的是一个个属性值。例如:addAttributes("a", "href", "class")表示:给标签a添加href和class属性,即允许标签a包含href和class属性。如果想给每一个标签添加一组属性,使用:all。例如:addAttributes(":all", "class").即给每个标签添加class属性。
addEnforcedAttribute(String tag, String attribute, String value) 给标签添加强制性属性,如果标签已经存在了要添加的属性,则覆盖原有值。tag:标签;key:标签的键;value:标签的键对应的值。例如:addEnforcedAttribute("a", "rel", "nofollow")表示
addProtocols(String tag, String key, String...protocols) 给URL属性添加协议。例如:addProtocols("a", "href", "ftp", "http", "https")标签a的href键可以指向的协议有ftp、http、https
addTags(String... tags) 向Whitelist添加标签
basic() 允许的标签包括: a, b, blockquote, br, cite, code, dd, dl, dt, em, i, li, ol, p, pre, q, small, strike, strong, sub, sup, u, ul,以及合适的属性。标签a指向的连接可以是 http, https, ftp, mailto,转换完后会强制添加 rel=nofollow这个属性。不允许包含图片。
basicWithImages() 在basic的基础上增加了图片的标签:img以及使用src指向http或https类型的图片链接。
none() 只保留文本,其他所有的html内容均被删除
preserveRelativeLinks(booleanpreserve) false(默认):不保留相对地址的url;true:保留相对地址的url
relaxed() 允许的标签:a, b, blockquote, br, caption, cite, code, col, colgroup, dd, dl, dt, em, h1, h2, h3, h4, h5, h6, i, img, li, ol, p, pre, q, small, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, u, ul。结果不包含标签rel=nofollow,如果需要可以手动添加。
simpleText() 只允许:b, em, i, strong, u。

四、例子

基于springboot

pom.xml依赖

<dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- jsoup -->
    <dependency>
      <groupId>org.jsoup</groupId>
      <artifactId>jsoup</artifactId>
      <version>1.13.1</version>
    </dependency>

    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
    </dependency>

    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.6</version>
    </dependency>

  </dependencies>

HtmlFilter过滤类

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.safety.Whitelist;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.List;

/**
 * HtmlFilter
 *
 * @author 撸小鱼
 * Created by lofish@foxmail.com on 2020-04-12
 */
public class HtmlFilter {

  /**
   * 默认使用relaxed()
   * 允许的标签: a, b, blockquote, br, caption, cite, code, col, colgroup, dd, dl, dt, em, h1, h2, h3, h4, h5, h6, i, img, li, ol, p, pre, q, small, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, u, ul。结果不包含标签rel=nofollow ,如果需要可以手动添加。
   */
  private Whitelist whiteList;


  /**
   * 配置过滤化参数,不对代码进行格式化
   */
  private Document.OutputSettings outputSettings;


  private HtmlFilter() {
  }

  /**
   * 静态创建HtmlFilter方法
   * @param whiteList 白名单标签
   * @param pretty 是否格式化
   * @return HtmlFilter
   */
  public static HtmlFilter create(Whitelist whiteList, boolean pretty) {
    HtmlFilter filter = new HtmlFilter();
    if (whiteList == null) {
      filter.whiteList = Whitelist.relaxed();
    }
    filter.outputSettings = new Document.OutputSettings().prettyPrint(pretty);
    return filter;
  }

  /**
   * 静态创建HtmlFilter方法
   * @return HtmlFilter
   */
  public static HtmlFilter create() {
    return create(null, false);
  }

  /**
   * 静态创建HtmlFilter方法
   * @param whiteList 白名单标签
   * @return HtmlFilter
   */
  public static HtmlFilter create(Whitelist whiteList) {
    return create(whiteList, false);
  }

  /**
   * 静态创建HtmlFilter方法
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的特定标签
   * @param pretty   是否格式化
   * @return HtmlFilter
   */
  public static HtmlFilter create( List<String> excludeTags,List<String> includeTags, boolean pretty) {
    HtmlFilter filter = create(null, pretty);
    //要过滤的标签
    if (includeTags != null && !includeTags.isEmpty()) {
      String[] tags = (String[]) includeTags.toArray(new String[0]);
      filter.whiteList.removeTags(tags);
    }
    //例外标签
    if (excludeTags != null && !excludeTags.isEmpty()) {
      String[] tags = (String[]) excludeTags.toArray(new String[0]);
      filter.whiteList.addTags(tags);
    }
    return filter;
  }


  /**
   * 静态创建HtmlFilter方法
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的特定标签
   * @return HtmlFilter
   */
  public static HtmlFilter create(List<String> excludeTags,List<String> includeTags) {
    return create( includeTags, excludeTags, false );
  }

  /**
   * @param content 需要过滤内容
   * @return 过滤后的String
   */
  public String clean(String content) {
    return Jsoup.clean(content, "", this.whiteList, this.outputSettings);

  }

  public static void main(String[] args) throws FileNotFoundException, IOException {
    String text = "<a href=\"http://www.baidu.com/a\" onclick=\"alert(1);\"></a><script>alert(0);</script><b style=\"xxx\" onclick=\"<script>alert(0);</script>\">abc</>";
    System.out.println(HtmlFilter.create().clean(text));
  }
}

XssFilter过滤器

import org.apache.commons.lang3.StringUtils;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * XssFilter
 *
 * @author 撸小鱼
 * Created by lofish@foxmail.com on 2020-04-12
 */
public class XssFilter implements Filter {

  /**
   * 例外urls
   */
  private List<String> excludeUrls = new ArrayList<>();

  /**
   * 例外标签
   */
  private List<String> excludeTags = new ArrayList<>();

  /**
   * 需要过滤标签
   */
  private List<String> includeTags = new ArrayList<>();

  /**
   * 开关
   */
  public boolean enabled = false;

  /**
   * 编码
   */
  private String encoding = "UTF-8";

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    String enabledStr = filterConfig.getInitParameter("enabled");
    String excludeUrlStr = filterConfig.getInitParameter("urlPatterns");
    String excludeTagStr = filterConfig.getInitParameter("excludes");
    String includeTagStr = filterConfig.getInitParameter("includes");
    String encodingStr = filterConfig.getInitParameter("encoding");

    if (StringUtils.isNotEmpty(excludeUrlStr)) {
      String[] url = excludeUrlStr.split(",");
      Collections.addAll(this.excludeUrls, url);
    }

    if (StringUtils.isNotEmpty(excludeTagStr)) {
      String[] url = excludeTagStr.split(",");
      Collections.addAll(this.excludeTags, url);
    }

    if (StringUtils.isNotEmpty(includeTagStr)) {
      String[] url = includeTagStr.split(",");
      Collections.addAll(this.includeTags, url);
    }

    if (StringUtils.isNotEmpty(enabledStr)) {
      this.enabled = Boolean.parseBoolean(enabledStr);
    }

    if (StringUtils.isNotEmpty(encodingStr)) {
      this.encoding = encodingStr;
    }

  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse resp = (HttpServletResponse) response;
    if (handleExcludeUrls(req, resp)) {
      chain.doFilter(request, response);
      return;
    }

    XssHttpServletRequestWrapper xssRequest = new XssHttpServletRequestWrapper((HttpServletRequest) request, encoding, excludeTags, includeTags );
    chain.doFilter(xssRequest, response);

  }

  private boolean handleExcludeUrls(HttpServletRequest request, HttpServletResponse response) {
    if (!enabled) {
      return true;
    }
    if (excludeUrls == null || excludeUrls.isEmpty()) {
      return false;
    }
    String url = request.getServletPath();
    for (String pattern : excludeUrls) {
      Pattern p = Pattern.compile("^" + pattern);
      Matcher m = p.matcher(url);
      if (m.find()) {
        return true;
      }
    }
    return false;
  }
}

一般情况下,我们都是通过request的parameter来传递参数。
但是,如果在某些场景下面,通过requestBody体(json等),来传递相应参数应该怎么办?
这就要需要我们对request的inputStream来进行来过滤处理了

有个地方需要注意一下的:
servlet中inputStream只能一次读取,后续不能再次读取inputStream。Xss过滤器中读取了stream之后,后续如果其他逻辑涉及到inputStream读取,会抛出异常。那我们就需要想办法把已经读取的stream,重新放回到请求中。

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.StringUtils;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;


/**
 * XSS过滤处理
 * @author 撸小鱼
 * Created by lofish@foxmail.com
 */
public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper{

  HttpServletRequest orgRequest;

  String encoding;

  HtmlFilter htmlFilter;

  private final static String JSON_CONTENT_TYPE = "application/json";

  private final static String CONTENT_TYPE = "Content-Type";


  /**
   * @param request HttpServletRequest
   * @param encoding 编码
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的标签
   */
  public XssHttpServletRequestWrapper( HttpServletRequest request, String encoding, List<String> excludeTags, List<String> includeTags ){
    super( request );
    orgRequest = request;
    this.encoding = encoding;
    this.htmlFilter = HtmlFilter.create( excludeTags, includeTags );
  }

  /**
   *
   * @param request HttpServletRequest
   * @param encoding 编码
   */
  public XssHttpServletRequestWrapper( HttpServletRequest request, String encoding ){
    this( request, encoding, null, null );
  }

  private String xssFilter( String input ){
    return htmlFilter.clean( input );
  }

  @Override
  public ServletInputStream getInputStream() throws IOException{
    // 非json处理
    if( !JSON_CONTENT_TYPE.equalsIgnoreCase( super.getHeader( CONTENT_TYPE ) ) ){
      return super.getInputStream();
    }
    InputStream in = super.getInputStream();
    String body = IOUtils.toString( in, encoding );
    IOUtils.closeQuietly( in );

    //空串处理直接返回
    if( StringUtils.isBlank( body ) ){
      return super.getInputStream();
    }

    // xss过滤
    body = xssFilter( body );
    return new RequestCachingInputStream( body.getBytes( encoding ) );

  }

  @Override
  public String getParameter( String name ){
    String value = super.getParameter( xssFilter( name ) );
    if( StringUtils.isNotBlank( value ) ){
      value = xssFilter( value );
    }
    return value;
  }

  @Override
  public String[] getParameterValues( String name ){
    String[] parameters = super.getParameterValues( name );
    if( parameters == null || parameters.length == 0 ){
      return null;
    }

    for( int i = 0; i < parameters.length; i++ ){
      parameters[i] = xssFilter( parameters[i] );
    }
    return parameters;
  }

  @Override
  public Map<String, String[]> getParameterMap(){
    Map<String, String[]> map = new LinkedHashMap<>();
    Map<String, String[]> parameters = super.getParameterMap();
    for( String key : parameters.keySet() ){
      String[] values = parameters.get( key );
      for( int i = 0; i < values.length; i++ ){
        values[i] = xssFilter( values[i] );
      }
      map.put( key, values );
    }
    return map;
  }

  @Override
  public String getHeader( String name ){
    String value = super.getHeader( xssFilter( name ) );
    if( StringUtils.isNotBlank( value ) ){
      value = xssFilter( value );
    }
    return value;
  }

  /**
   * <b>
   * #获取最原始的request
   * </b>
   */
  public HttpServletRequest getOrgRequest(){
    return orgRequest;
  }

  /**
   * <b>
   * #获取最原始的request
   * </b>
   * @param request HttpServletRequest
   */
  public static HttpServletRequest getOrgRequest( HttpServletRequest request ){
    if( request instanceof XssHttpServletRequestWrapper ){
      return ((XssHttpServletRequestWrapper) request).getOrgRequest();
    }
    return request;
  }

  /**
   * <pre>
   * servlet中inputStream只能一次读取,后续不能再次读取inputStream
   * xss过滤body后,重新把流放入ServletInputStream中
   * </pre>
   */
  private static class RequestCachingInputStream extends ServletInputStream {
    private final ByteArrayInputStream inputStream;
    public RequestCachingInputStream(byte[] bytes) {
      inputStream = new ByteArrayInputStream(bytes);
    }

    @Override
    public int read() throws IOException {
      return inputStream.read();
    }

    @Override
    public boolean isFinished() {
      return inputStream.available() == 0;
    }

    @Override
    public boolean isReady() {
      return true;
    }

    @Override
    public void setReadListener( ReadListener readListener ){
    }
  }
}

springboot2.2.4.RELEASE中注册Filter

@Configuration
public class XssFilterConfig {

  @Value("${xss.enabled:true}")
  private String enabled;

  @Value("${xss.excludes:}")
  private String excludes;

  @Value("${xss.includes$:}")
  private String includes;

  @Value("${xss.urlPatterns:/*}")
  private String urlPatterns;

  @Bean
  public FilterRegistrationBean<XssFilter> xssFilterRegistrationBean() {
    FilterRegistrationBean<XssFilter> registration = new FilterRegistrationBean<>();
    registration.setDispatcherTypes(DispatcherType.REQUEST);
    registration.setFilter(new XssFilter());
    registration.addUrlPatterns(urlPatterns.split(","));
    registration.setName("XssFilter");
    registration.setOrder(Integer.MAX_VALUE);
    Map<String, String> initParameters = new HashMap<String, String>();
    initParameters.put("excludes", excludes);
    initParameters.put("includes", excludes);
    initParameters.put("enabled", enabled);
    registration.setInitParameters(initParameters);
    return registration;
  }
}

测试

http://localhost:8080/demo/th/xss?abc=%3Ca%20href=%22http://www.baidu.com/a%22%20onclick=%22alert(1);%22%3Eabc%3C/a%3E%3Cscript%3Ealert(0);%3C/script%3E&abc=%3Cb%20style=%22xxx%22%20onclick=%22%3Cscript%3Ealert(0);%3C/script%3E%22%3Eabc%3C/%3E


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